Erosion protection for wells



Jan. 23, 1968 B. c. ARNWINE EROSION PROTECTION FOR WELLS Filed March 30, 1966 FIG.2

FIG.

FIG. 4

FIG. 3

BENNIE C. ARNWINE INVENTOR m 7 ATTORNEY United States Patent 3,365,090 ERGSEON PROTECTION FQR W'ELLS Bennie C. Arnwine, Dallas, Tex., assignor to Mobil Oil Corporation, a corporation of New York Filed Mar. 30, 1966, Ser. No. 538,848 16 Claims. (Cl. 166-243) ABSTRACT OF THE DISCLOSURE This specification discloses well apparatus for alleviating erosion of well tubing. A plurality of protective members are slidably mounted on the tubing at a location where detrital material entering the well may cause erosion of the tubing. At least some of the protective memers disengage from the tubing upon undergoing a specified amount of erosion. Thus, the protective members are replenished as they become eroded and provide protection for the tubing over a prolonged period of time. A disclosed form of protective member comprises a sleeve which includes a continuous retaining member and a discontinuous shield. When the protective sleeve is eroded to an extent such that the retaining member is parted, the sleeve is disengaged from the tubing.

This invention relates to the production of subterranean fluids through wells, and more particularly to apparatus for alleviating erosion of downhole well equipment by detrital material contained in such subterranean fluids.

In the petroleum industry, downhole well equipment often is subjected to erosion due to the abrasive action of detrital material such as unconsolidated sand grains entrained in petroleum fluids as they enter the well. This problem most often is encountered in multiply completed wells which produce fluids from two or more levels in a well. The most common multiply completed wells are dual-completion wells in which oil or gas is produced from two vertically spaced subterranean formations. A conventional manner of dually producing such formations is to set and cement casing through both formations and then set a casing packer between the formations. A tubing string is extended through the packer with its lower open end landed adjacent the lower productive formation. The casing packer thus effectively seals off the annular space between the tubing and casing and isolates the lower formation, which is in fluid communication with the intcrior of the tubing string. The fluid from the lower formation thus flows through the tubing and to the surface of the well or wellhead separately from the fluid from the upper formation which is produced through perforations in the casing into the annulus between the casing and the tubing string. The fluid from the upper formation flows to the wellhead either directly through the annulus or through an additional tubing string.

Another form of dual-completion well is the so-called slim hole dually completed Well. In this arrangement the well is not cased in the conventional manner and two parallel strings of tubing or small casing are cemented in the well. Each tubing string is selectively perforated at the level of one of the subterranean formations and each formation is produced separately through its respective tubing string.

In either form of multiple completion, a section of pipe such as well tubing will extend past a productive formation and thus be exposed to the produced subterranean fluid as it enters the well either through perforations in the wall of the casing, as in the first above-described arrangement, or through the perforations in the wall of the tubing itself, as in the second above-described arrangement. The fluid usually is under substantial pressure and passes from the productive formation through the restricted perforations in the casing or tubing at high velocity and in jetted streams. This particularly is true where the fluid being produced is comprised primarily of gas. Such fluid often has a content of sand or other particulate detrital material which impinges against the pipe surface adjacent the perforations. Such detrital material entrained in the incoming fluid abrades and erodes the pipe surface, thus leading to pipe failure, and also intensifying the corrosion of the pipe.

In the past, numerous means have been employed in attempts to protect tubing surfaces and alleviate the erosion thereof. One technique involves the wrapping of layers of lead around the tubing on the theory that a malleable material would absorb some of the kinetic energy of the detrital material more readily than the tubing itself. Alternatively, hard, brittle material such as ceramics and glass and resilient materials such as rubber have been employed as protective materials for the tubing. While such techniques have met with some success, the resilient coatings usually being the most effective, none of these techniques has proven entirely satisfactory.

One difficulty experienced with the heretofore practiced procedures resides in the fact that the materials used, even though sometimes more resistant to the abrasive action of the detrital material than the metal pipe surfaces, still experience some erosion and ultimately fail, leaving the pipe surfaces exposed. This of course necessitates expensive workovers such as withdrawing the tubing, repairing it if necessary, and providing additional protective material.

In accordance with the instant invention, there is provided a new and improved system for alleviating erosion of an elongated member such as a piece of tubing which is adapted for insertion into a well and which has a surface subject to erosion by detrital material. A plurality of protective members are slidably mounted on the surface of the elongated member and supported on a stop member extending laterally therefrom. At least some of these protective members include means responsive to a specified amount of erosion thereof for disengaging the protective member from the metal surface. Thus, when the elongated member is inserted in place in the well, the protective members continually are replenished as they undergo a specified amount of erosion due to the abrasive action of the incoming detrital material.

A preferred embodiment of the present invention is utilized in a well traversing a subterranean formation from which it is desired to recover fluid such as petroleum gases. The well has a conduit therein with an open production interval opposite the subterranean formation. The open production interval may be defined by a plurality of perforations as will be recognized by those skilled in the art. For example, the open production interval may be formed by gun-perforating a section of the casing adjacent the producing formation. In producing the well, fluid is flowed through the open production interval in the casing and thence upwardly within the casing to the surface of the Well. A second conduit such as a tubing string is disposed Within the first conduit opposite the open production interval whereby the outer surface of the second conduit is subject to abrasive action of the detrital material entrained in the production fluids.

In accordance with the instant invention, a plurality of protective sleeves are slidably mounted on the outer surface of the second conduit opposite the open production interval. At least some of the protective sleeves include a continuous retaining member which extends transversely of the second conduit about the outer perimeter thereof. The protective sleeves further comprise a discontinuous inner shield member interposed between the retaining member and the surface of the second conduit. Both the retaining member and the inner shield are biased outwardly away from the outer surface of the second conduit such that they are disengaged from the second conduit when the retaining member is parted due to the abrasive action of the detrital material. Thus, the protective sleeve will be disengaged from the outer conduit surface when subjected to a specified amount of erosion. As a particular protective sleeve thus is disengaged from the conduit, another sleeve slidably disposed on the outer surface of the conduit falls into place and replaces the sleeve thus disengaged. Thus, effective erosion protection is continuously provided for the metal tubing surface in the 'well opposite the open production interval, thus greatly increasing the time between workovers of the well or sometimes making such workovers unnecessary.

For a better understanding of the instant invention,

reference may be had to the following detailed description taken in conjunction with the accompanying drawings in which:

FIGURE 1 is an elevation partly in section illustrating a preferred form of the invention as embodied in a well assembly;

FIGURE 2 is a plan view in section illustrating one form of protective sleeve;

FIGURE 3 is a cross-sectional view taken along line 3-3 of FIGURE 2 and illustrates one form of protective sleeve construction;

FIGURE 4 is a sectional view similar to FIGURE 3 showing an alternate form of protective sleeve construction; and

FIGURE 5 is a plan view showing a modified form of protective sleeve. 9

With reference to FIGURE 1, there is shown a well bore 1t traversing a productive formation 12 and provided with a first conduit or casing string 14. The casing is cemented as indicated at 15 and the casing and surrounding cement sheath are provided with a plurality of perforations 17 which define an open production interval as indicated by brackets 18. Although in mostwells in which the present invention is utilized, the open production interval will be defined by a plurality of circular perforations formed by jet or gun-perforating techniques, it will be understood that other suitable arrangements may be used. For example, the open production interval may be formed by so-called shop perforated or slotted pipe in which the openings are formed prior to insertion of the casing into the Well. Also, the open production interval may be defined by one or more narrow longitudinally extending openings within the casing 14 and cement 15. Such procedures of opening a casing to the flow of subterranean fluids are well known in the art and will not be described further. It will be understood, however, that the term open production interval as used herein and in the appended claims is intended to cover all such means of providing a flow path for the ingress of fluids from the exterior of the casing.

A packer 19 is disposed between the productive formation 12 and a lower productive formation (not shown) in order to isolate these formations from'one another so that there is no communication between these formations within the well. A production tubing string 20 is disposed in the well as illustrated and extends from the wellhead 21 and is landed at a level (not shown) below the packer 19, usually adjacent the lower productive formation. Fluids from the lower productive formation thus are produced through the interior of the tubing string 20 and carried to the surface of the well where they pass into a suitable gathering line 29a.

A second packer 22 is provided between the tubing string 20 and casing 14 at a point above the top of the productive formation 12. A second tubing string 24 extends from the surface of the well and through the second packer 22 as shown. As is apparentfrom the drawing, the second tubing string 24 provides a production passage to the surface of the well for fluids produced from the proent invention. Also, it will be understood that the arrangement thus far described is exemplary only and that other suitable arrangements may be used. For example, tubing 24 and packer 22 may be dispensed with and fluids from the productive formation 12 may be produced to the surface of the well directly through the annular space defined by the tubing 20 and the casing 14. Alternatively, tubing string it) may not extend to the wellhead, but instead may terminate within or above packer 22, in which case fluid from the lower formation will pass from tubing 20 into the space between tubing 24 and casing 14 and thence upwardly to the wellhead. Also, while only a single casing string 14 is shown, it will be understood that the Well may be provided with a plurality of easing strings. For example, the well may be provided with a suit able conductor pipe or surface string and one or more intermediate strings as will be understood by those skilled in the art. Irl addition, while the casing 14 in FIGURE 1 is shown as extending completely to the surface of the well, it will be understood that other suitable arrangements may be used. Forexample, the perforated outer conduit may take the form of a liner which is suspended from or otherwise extends into a casing string. Also, the perforated conduit may take the form of a socalled scab liner which does not extend up into a casing string but simply rests upon the bottom of the borehole and is cemented therein in accordance with conventional practices. In this case, all or part of the well above the perforated liner may be uncased. Such completion practices are well known to those skilled in the art and therefore will not be described further.

In accordance with the instant invention, there is provided around the outer surface of tubing 20 and adjacent the open production interval 13a column comprised of a plurality of protective sleeves 26. The protective sleeves 26 are slidably mounted on the outer surface of tubing 20 and are supported against downward movement therealong by means of a suitable stop member 28 fixedly secured to the outer surface of the tubing and extending laterally thereof. The stop member 28 conveniently may take the form of a conventional tubing collar having a diameter at least greater than the inner diameter of the the abrasive action of the detrital material entrained in the production fiuid. As a particular sleeve such as sleeve 26a is eroded by a specified amount, the sleeve is disengaged from the tubing surface by means hereinafter described and falls downwardly through the annulus between tubing 20 and casing 14 until it reaches the upper surface of packer 19 or other suitable means obstructing the annulus. Upon the disengagement of sleeve 26a from the tubing surface, the next adjacent sleeve 261) will move downwardly until it occupies the position occupied by sleeve 26a, thus providing continuous erosion protection for the outer surface of tubing 20.

It is preferred to lubricate the outer surface of tubing 26 along which the sleeves 26 are disposed and in many cases the sleeves will slide downwardly along the'tubing surface by their own weight. However, in those instances where the sleeves are made of a relatively light material such as certain plastics, it will be preferred to provide means for biasing the sleevesdownwardly along the tubing. As shown in FIGUREI, such means may take the form of an annular plate 36 which is slidablydisposed on the tubing 29 adjacent the top of the column of sleeves 26. The plate 39 may be formed of a relatively heavy material so that the weight thereof exerts suflicient downward force on the column of sleeves, Preferably, the plate will be provided with means biasing the plate itself downwardly. Such means may take the form of a plurality of coil springs 32 compressibly interposed between the plate 313 and a tubing collar 34 or other suitable means fixedly secured to the outer surface of the tubing 29.

Turning now to FIGURE 2, there is shown one form of protective member 26 which may be utilized in the instant invention. More particularly, and with reference to FIGURE 2, there is shown a protective member in the form of an annular sleeve which includes a retaining member 38 and an erosion-resistant shield 39 comprised of an inner shield member 40, which is adapted to be interposed between the retaining member and the tubing surface to be protected, and an outer shield member 42. The retaining member 38 is continuous and functions to hold the protective member on the tubing outer surface or other surface to be protected. In the embodiment of FIGURE 2, the retaining member is made continuous by locking the ends thereof together with a suitable detent connection 41. It will be understood, however, that the ends of the retaining member may be connected by other suitable means such as welding or that it may be molded or cast as an integrally continuous body.

The shield 39 preferably is of unitary construction so that the inner and outer shield members 40 and 42, respectively, are merely different portions of one integral element. For example, the shield 39 may take the form of an elongated plastic member having an interior passageway extending longitudinally thereof for insertion of the retaining member 38. Thus, in constructing the protective sleeve shown in FIGURE 2, the retaining member may be inserted through the passage of shield 39 and then shaped to the circular configuration shown and the ends thereof secured together by means of the locking connection 41.

The erosion-resistant shield 39 is discontinuous. That is, the ends of the shield are not connected although preferably they meet in an abutting relationship as shown at 43. The retaining member 38 and the shield 39 are biased outwardly such that upon partition of the retaining member the entire assembly will spring outwardly away from the outer tubing surface. This preferably is accomplished by prestressing the retaining member 38 in tension. For example, the retaining member may take the form of a normally straight band of spring steel which when formed in the circular configuration shown is stressed outwardly. Alternatively, the retaining member 38 may take the form of a flexible nonstressed member and the shield 39 may be stressed in tension such that the shield and also the retaining member 38 are biased outwardly. Regardless of the means employed to impart an outward bias to the protective sleeve 26, it will be recognized from the drawing that the impingement of detrital material upon the sleeve will first erode away a portion of the outer member 42 of the shield 39. The shield will be eroded until ultimately the retaining member 38 will be exposed to the abrasive action of the detrital material. Thereafter, the further eroding action of the detrital material ultimately will cause partition of the retaining member 38 whereupon the entire sleeve assembly will spring outwardly from the tubing and the above next adjacent protective member will take its place. In addition to outward bias imparted, for example, by a stressed retaining member 38, the action of the high-velocity fluid streams entering through perforations 17 will tend to force the parted sleeve away from the tubing surface.

An important feature of the instant invention resides in the fact that if retaining member 38 is perforated under the abrasive action of the detrital material but not parted, the protective sleeve still will offer erosion protection for the tubing or other surface on which the protective sleeve is mounted. This is due to the portion of the erosionresistant shield, i.e., inner shield member 40, which is interposed between the retaining member 38 and the tubing surface. In accordance with a preferred embodiment of the invention, an assembly is provided wherein a central portion of the outer shield member 42 disposed adjacent the retaining member is less erosion protective than the vertically adjacent portions of the outer shield member 42. Thus, the shield member 42 will preferentially erode in a manner such that the retaining member 38 is subject to erosion before the inner shield member 49. This feature of the invention is shown in FIGURES 3 and 4.

Turning first to FIGURE 3, there is shown a crosssectional view of the annular sleeve 26 taken along line 33 of FIGURE 2. As can be seen in FIGURE 3, the outer surface of that portion of shield member 42 which lies in a horizontal plane common with the retaining member 38 is recessed inwardly at 46 in order to form a central shield portion of less lateral width than the vertically adjacent portions of the shield which do not lie in such a plane. As will be apparent from an examination of FIGURE 3, the central portion of the shield member will, by nature of its reduced width, erode down to the level of the retaining member before the adjacent portions.

With regard to FIGURE 4, there is shown another form of protective shield in which the central portion of the outer shield member disposed adjacent the retaining member is less erosion protective than the vertically adjacent sections thereof. In this embodiment, an erosion-resistant shield 58 is provided with an insert 52 which is formed of a more easily erodable material than the remaining portions of the shield. Therefore, erosion will preferentially take place within the central portion of the shield defined by insert 52, thus exposing retaining member 38 to the abrasive action of the detrital material before so exposing of the vertically adjacent portions of the inner portion of shield member Stl. Although not so shown, the portion of the erosion-resistant shield defined by insert 52 may be provided with a recessed surface similarly as shown in FIGURE 3.

In another embodiment of the invention, there is provided a protective sleeve employing et another feature which will insure that partition of the retaining member will occur before perforation of the inner shield member. In this aspect of the invention, the retaining member 38 is formed of a material which is less resistant to erosion than the material forming the protective shield and particularly the inner shield member. Thus, regardless of the manner in which the outer surface of the erosion-resistant shield erodes, the retaining member will be parted in relatively short order once it is exposed to the abrasive action of the detrital material. It is preferred to employ this feature of the invention regardless of the nature of the erosion-resistant shield. Thus, even though the shield embodies means such as recessed groove 46 of FIGURE 3 or insert 52 of FIGURE 4 which causes the shield to erode preferentially adjacent the retaining member 38, such member still will be formed of a material exhibiting relatively low erosion resistance.

In order to insure further against premature perforation of the inner shield member, it is preferred that the lateral width of such member be at least equal to the lateral width of the retaining member. Referring to FIG- URE 3, for example, the width W of inner member 49 should be at least as great, and preferably greater, than the width W of retaining member 38.

In the form of protective sleeve shown in FIGURE 2, the erosion-resistant shield is formed of a single elongated member. In a modified form of protective sleeve shown in FIGURE 5, the erosion-resistant shield is segmented in order to facilitate disengagement of the sleeve from the tubing surface upon partition of the retaining member. More particularly, and with reference to FIGURE 5, there is shown an annular sleeve 56 comprising an erosionresistant shield 58 and a continuous retaining member 60 indicated by broken lines. The shield 58 is formed of a plurality of segments 62, each in abutting relationship with an adjacent segment. Thus, even though the shield 58 1s for-med of a rigid material having little elasticity, it will disengage easily from the protected surface upon partition of the retaining member. It will be recognized that in this embodiment the retaining member 60 must be stressed in order to impart a potential outward bias to the sleeve assembly. The shield 58 of FIGURE 5 is otherwise similar to that previously described. For example, the shield may be provided with a recessed surface as indicated by broken line 64 which is similar to that indicated in FIGURE 3 by reference numeral 45.

The various components of the protective sleeves utilized in the instant invention may be formed of any suitable materials. High impact resistant polypropylene exhibits good erosion-resistant properties and it has been found that under conditions encountered in most producing wells such polypropylene is more resistant to erosion by sand or other detrital material than steel. Thus, in the embodiment of FIGURE 3, for example, the erosion-resistant shield 39 may be formed of high impact resistant polypropylene and the retaining member 38 may take the form of a stressed steel ring. In the embodiment of FIG- URE 4, the erosion-resistant shield and the retaining member may be formed of these same materials and the insert 52 may be formed of neoprene or other suitable plastic which is less erosion-resistant than polypropylene.

Referring again to FIGURE 1, the annular plate member 3t) will function to provide erosion protection for tubing when it ultimately reaches a position opposite the open production interval. The outer surface of member thus may be formed of polypropylene or material exhibiting good erosion-resistant properties. However, the annular plate 39 need not be provided with the disengaging feature of sleeves 26 since no additional protective members are disposed abovethis plate.

The length of the column of erosion protective members will depend upon various factors such as the erosion experience of the well involved, the material of which the shield members and retaining members are made, and the desired minimum time between workovers of the well. While these and other factors will vary considerably from Well to well, in order to provide an adequate level of continuous erosion protection, the column in practically all cases should be long enough to supply a reservoir of protective members at least equal to the number of protective members disposed adjacent the open production interval. Thus, it is preferred in practicing the instant invention to utilize a column of erosion protective members which extends above the open production interval by a distance at least as great as the length of the open production interval. In many instances of course it may be desirable to employ a column of greater size.

Having described certain specific embodiments of the instant invention, it will be understood that further modifications thereof may be suggested to those skilled in the art, and it is intended to cover all such modifications as fall within the scope of the appended claims.

Vlhat is claimed is:

1. In an erosion protective assembly for use in alleviating erosion due to detrital material entrained in subterranean fluids:

an elongated member adapted for insertion into a well and having a surface subject to erosion by said detrital material, said elongated member having a stop member fixedly secured thereto and extending laterally from said surface; and

a plurality of protective members slidably mounted on said surface and supported on said stop membenat least some of said protective members each including means responsive to a specified amount of erosion of said each of said protective members for disengaging said each of said protective members from said surface of said elongated member.

2. The assembly of claim 1 wherein said disengaging means of said each of said protective members comprises a continuous retaining member extending about a transverse perimeter of said elongated member and normally retaining said each of said protective members on said surface, said retaining member being biased away from said surface whereby said each of said protective members is disengaged from said surface when said continuous relative to said surface.

5. In a well adapted for the production of subterranean fluids, an assembly for alleviating erosion of downhole equipment, comprising:

a first conduit disposed in said well, said conduit having an open production interval therein adaptedfor the passage of subterranean fluids into the interior of said conduit;

a second conduit of a smaller size than said first conduit disposed within said first conduit opposite said open production interval; and V a plurality of protective sleeves slidably mounted on the outer surface of said second conduit opposite said open production interval, at least some of said protective sleeves each including means responsive to a specified amount of erosion of said each of said protective sleeves for disengaging said each of said protective sleeves from said outer surface of said second conduit.

6. The assembly of claim 5 wherein said disengaging means of said each of said protective sleeves comprises a continuous retaining member extending transversely of said second conduit about the outer perimeter of. said second conduit and normally retaining said each of said protective members on said second conduit, said retaining member being biased outwardly from the outer surface of said second conduit whereby said each of said protective sleeves is disengaged from said second conduit when said continuous member is parted.

7. The assembly of claim 6 wherein said each of said protective sleeves comprises a discontinuous inner shield interposed between said retaining member and the outer surface of said conduit and biased outwardly fromsaid outer surface.

8. The assembly of claim 7 wherein said each of said protective sleeves further comprises an outer shield mern- V ber interposed between said retaining member and said first conduit.

9. In a well adapted for the production of subterranean a conduit disposed in said well, said conduit having an open production interval therein adapted for the I passage of subterranean fluids into the interior of said conduit;

2. second conduit of a smaller size than said first conduit disposed within said first conduit opposite said open production interval and extending to a level above said open production interval; and

a plurality of annular protective sleeves slidably mounted on the outer surface of said second conduit opposite said open production interval and extending to a level on said second conduit above the top of said open production interval, at least some of said protective sleeves each including an annular continuous retaining member disposed about said second conduit and an annular discontinuous protective shield mounted on said retaining member, said shield comprising an outer shield member interposed between said retaining member and said first conduit and an inner shield member interposed between said retaining member and said second conduit whereby perforation of said continuous member will not expose said second conduit to erosion.

10. The assembly of claim 9 wherein said continuous retaining member is stressed to bias said retaining member and said shield outwardly from the outer surface of said second conduit whereby said discontinuous annular shield and said continuous member are disengaged from said second conduit when said continuous member is parted.

11. The assembly of claim 10 wherein said retaining member is formed of a more easily erodable material than the inner member of said shield.

12. The assembly of claim 10 wherein the lateral width of said inner member of said protective shield is at least as great as the lateral width of said retaining member.

13. The assembly of claim 10 wherein said protective shield comprises a plurality of segments in abutting relationship with one another.

14. The assembly of claim 10 wherein a portion of said outer member of said shield lying in a common plane with said retaining member is less resistant to erosion than the adjacent portions of said outer member.

15. The assembly of claim 14 wherein said less resistant portion of said outer member is formed of a more easily erodable material than said adjacent portions of said outer member.

16. The assembly of claim 14 wherein the lateral width of said less resistant portion of said outer member is less than the lateral width of said adjacent portions of said outer member.

References Cited UNITED STATES PATENTS 2,925,097 2/ 1960 Duesterberg 166-243 3,034,912 5/1962 Flowers 166-243 3,070,166 12/1962 Knauth 166-243 X 3,070,171 12/ 1962 Rike et al. 166-243 3,073,393 1/1963 Smith 166-243 3,075,582 1/1963 Morse et al 166-46 3,129,982 4/ 1964 Fawick 166-241 3,220,437 11/ 1965 Salford 166-242 X CHARLES E. OCONNELL, Primary Examiner.

DAVID H. BROWN, Examiner. 

